The cellular machinery that generates endogenous temporal control and organization known collectively as the biological clock, exists in virtually all eukaryotic organisms. The clock influences many aspects of human physiology including work-rest cycles, and drug tolerance band effectiveness, and its malfunction is known to be associated with common human disorders such as insomnia and manic-depressive illness. Extensive research in the past has demonstrated the extent and significance of clock control on cellular and organismal processes; however, the cellular and molecular basis of the biological clock and its control mechanisms are largely unknown. Therefore, the long-term goal of the study of the clock and clock regulation is to define the genetic and biochemical components of the clock, and understand how these components interact to keep functional time. This study will use molecular genetics to identify cis-acting elements and trans-acting factors conferring clock regulation using a simple eukaryotic model system, Neurospora crassa. First, minimal cis-acting DNA elements including a circadian clock-responsive element and a light- responsive element will be determined by deletion analysis of the 5' upstream regulatory region of the clock-controlled gene-1 (ccg-1). The minimal CCRE driving a selectable reporter such as hygromycin phosphotransferase will be then used in a genetic screen to identify the gene(s) encoding the trans-acting factors conferring morning-specific clock regulation. Characterization and functional studies of the identified factor(s) will lead to an understanding of the mechanism by which the clock exerts its control on the clock-controlled processes.